Yahoo! Does CSS
Yahoo! has a CSS front page in Beta mode. Thanks to Jeff from work for the link to WhiteSpace where they dig deep into the high and low points of the redesign.
One of the most interesting points for me in the article comes from the comments where Rimantas explains precisely when it is appropriate to include an external css (and presumably js) file versus including it inline.
I didn't realise that it is as simple as the size of the css or js chunk. Simply put: over 500 bytes including whitespace put it in a separate file else include it on the page. Why? 500 bytes is all that is required for a request to determine from the header if the page has changed. If your CSS/JS is larger than that you save {filesize_in_bytes-500} bytes per request thru this mechanism.
To verify that this is the case I was looking around and found an excellent reference on page caching with HTTP requests by Mark Nottingham. I scanned through the RFC2616 to try to get to the bottom of the max HTTP header size but couldn't find it anwhere. If anyone could provide a reference for me that would be great.